Ingredients and chemical composition of diets used in this study.

1Optigrain® (DEUKA, Deutsche Tiernahrung, Düsseldorf, Germany), consisting of hydrothermally processed wheat (50%), barley (25%) and corn (25%).2Corn starch in the basal diet was partially replaced in the diets containing 150, and 2500 mg/kg zinc with analytical grade zinc oxide (Sigma Aldrich, Deisenhofen, Germany) to adjust for the zinc level.3Mineral and Vitamin Premix (Spezialfutter Neuruppin Ltd., Neuruppin, Germany), containing per kg dry matter: 130 g Na (as sodium chloride), 55 g Mg (as magnesium oxide), 700,000 IU Vit A, 120,000 IU Vit D3, 8,000 mg Vit E, 300 mg Vit K3, 250 mg Vit B1, 250 mg Vit B2, 400 mg Vit B6, 2,000 µg Vit B12, 2,500 nicotinic acid, 100 mg folic acid, 25,000 µg biotin, 1,000 mg pantothenic acid, 80,000 mg choline chloride, 5,000 mg Fe (as iron-(II)-carbonate), 1,000 mg Cu (as copper-(II)- sulfate), 6,000 mg Mn (as manganese-(II)-oxide), 45 mg J (as calcium-iodate), 35 mg Se (as sodium-selenite).4Analyzed concentration of zinc in the basal diet without ZnO supplementation. The other diets contained 156, and 2355 mg/kg, respectively.